Process for stabilization of copper treated oils



Patented Nov. 19, 1940 UNITED. STATES PATENT OFFICE- 1 2,222,122 mousse ron s'ramuza'rrgn or corrsa,

Walter A. 8a.... and GrahamH. Short,

Bartlesville, Okla, assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application November 9, 1938,

Serial No. 239,731

4Claims.

stabilizing or preventing the deterioration of hydrocarbon oil which has undergone a purifying treatment with reagents containing copper.

Hydrocarbon oil, particularly petroleum distil latesusually contain impurities, including sulfur compounds, which cause the oil to exhibit undesirable properties such as bad odor and gum and color formation. It is customary, therefore, to subject said impure oil to a purifying treatment in order to remove the impurities or to convert them to less objectionable forms, for example, the conversion of mercaptans to disulfldes.

The methods of treatment for the removal or conversion of mercaptans make use of various chemical processes, and of these processes, one of the most satisfactory is the process utilizing copper, salts of copper, or solutions containing copper salts.

However, subsequent to treatment with coppercontaining reagents, it has been found that many hydrocarbon oils require further treatment or stabilization. This condition is due to the fact that said unstable oils retain from their contact with copper reagents, extremely small quantities of oil-soluble copper compounds. These traces of copper compounds remaining in the oil areresponsible for the marked acceleration of reactions which lead to the formation in said oil of color, gum, resinous deposits and polymers; these deteriorative changes seriously impair such properties of the oil as color, gum content and octane number.

One object of this invention is to eifect'the removal of traces of copper compounds from hydrocarbon oils.

I Another object of this invention is to prevent the deterioration of hydrocarbon oil which has stable with respect to sum formation subsequent to treatment with copper-containingreagents. A further object of this invention is the treatment of oil which retains traces-of copper compounds subsequent to sweetening with copper reagents, to removesaid copper from the oil, thereby delaying or preventing deterioration.

Another object of this invention'is to provide a min the sweetening of hydrocarbon'oil with copper reagents whereby the sweetened oil is stabilized against deterioration-by the removal therefrom of retained copper salts.

Another object of this invention is the conversion of oil-soluble copper compounds present 5 in hydrocarbon oil as a result of sweetening with copper reagents to oil-insoluble compounds, said conversion resulting in complete separation of the insoluble copper compounds from the oil.

Schulze and Frey in U. S. Patent'No. 1,980,555

described a method for stabilizing an oil treated with copper and which exhibited discoloring "and/or formation of resinous matter, polymers and oxidation products; that is, a method of stabilizing the oil by bringing it in contact. with an alkaline sulphide solution subsequent to treating with the copper reagent.

We have now discovered that copper treated oils may bestabilized by means other than the alkaline sulfide solution referred to above and that go .these meansinvolve certain improvements and advantages. This discovery is extremely important inthat it clearly defines the conditions which must be met to produce stabilized oils.-

This discovery likewise makes it possible to diand the second group consisting of those reagents so which will not remove sumcient quantities of the 3 copper compounds to stabilize the oil.

We have found that copper mercaptides increase in solubility in the oil withincreasing molecular weight of the mercaptans. Copper as methyl mercaptide is the most'insoluble of all the copper mercaptides and is almost totally insoluble in hydrocarbon oils. Copper ethyl mer-V captide, the next number in the series, is a little more soluble, yet its actual solubility figure is 40 extremely low. Cupper butyl mercaptides and amyl mercaptides are much more soluble and their solubilities-may be determined'in the usual manner of precise measurements.

-We have now discovered that hydrocarbon oil containing copper methyl mercaptide, and therefore completely'saturated with respect to the substance, does not show any of the undesirable re-.

actions mentioned above as resulting from the catalytic eflect of dissolved copper compounds. so

In other words, we have established that the cancentration of copper from a saturated solution of coppermethyl mercaptide in hydrocarbon oil is too low to cause deterioration of the oils. On

the other hand. we havefound that if the hydrols carbon is saturated with respect to copper ethyl mercaptide, the concentration of copper is just suflicient to cause a slow depreciation in the said properties of the oil. Thus, -we have established that there is a critical value for copper concentration in'the oil, above which deterioration will occur, and below which the oil will be stable as regards gum and color formation in storage.

This improved .process of stabilization depends on the eifective removal of traces of copper compounds from the contaminated hydrocarbon oil by treating said oil to completely convert the hydrocarbon oil-soluble copper compounds into compounds whose solubility is less than the solubility of the copper salt of ethyl mercaptan. By this means, and the subsequent separation of these more insoluble compounds from the hydrocarbon oil, the deterioration due to dissolved copper compounds in the oil is prevented.

Since the deterioration of oil is accelerated in a catalytic manner by dissolved copper salts, it toliows that copper salts more insoluble than copper ethyl mercaptide are inactive as catalysts for deteriorative reactions in oil, and likewise possess marked resistance to oxidation processes which would change said insoluble copper compounds to more active forms which would be injurious to the oil.

Oil-soluble copper compounds whichmay .be. formed in complex hydrocarbon oil mixtures,

particularly in petroleum distillates, are usually mercaptides or salts of acidic components such as cresylic and naphthenic acids.- Such compounds may be more soluble than copper ethyl aezarae ened with a cupric chloride solution may be removed by adding thereto a controlled amount of methyl mercaptan to convert the more soluble copper compounds into the less soluble copper methyl mercaptide. Complete removal of the copper is not effected by treatment of the oil with caustic soda, carbonate or phosphate solutions, or by the addition to the oil of controlled amounts of ethyl mercaptan.

In order to explain more exactly the criterion by which the stabilization of copper-containing oil is judged, the relative solubilities of the copper compounds encountered may be considered.

The sulfides of copper are the most insoluble compounds of the metal. The mercaptides by reason of analogous structure exhibit similar solubilities in water, but are slightly more soluble in oils due to the organic nature of the alkyl or aryl group present in the mercaptide molecule.

The sulfides of copper have a solubility of about 0.00033 gram per liter of water and an infinitesimal solubility in hydrocarbon oils; the solubility of copper methyl mercaptide is approximately 0.000003 gram per liter of cracked naphtha, or about one hundredth the solubility of copper sulfide in water. These solubility figures are based on extremely sensitive colorimetric tests, especially devised to indicate the presence and concentration of copper in hydrocarbon oil.

The following table shows the approximate solubilities of copper salts in oils, or the extent to which oil-soluble copper compounds are formed by contact of the oils with said copper salts for a 24 hour period.

TABLE I Oil-soluble copper Copper salt Hydrocarbon oil Dissolved copper compounds, grams per 1000 cc. of oil Parts per million Copper oxide Doctor-sweet cracked naphtha.. Greater than 1.. 0.0003 (approximate). Copper carbonate-(basic) do 0.0003 (approximate). Copper hydroxi do 0.0003 (approximate). Copper phosphate do do 0.0003 (approximate). Copper cyan dc (KCN Sol.).... do do 0.0003 (approximate). Copper silicate do 0.0003 (approximate). Copper sulfite. do do 0.0003 (approximate). Copper-n-butyl-mercaptrde. do 0.0003 (approximate). Copper-t-butyl-merca tide do 10,000.. .300. Copper-ethyl-mereapt de do 0.1 0.00003.

8p. gr. oi naphtha taken as 0.75.

mercaptide, and likewise may not be removed from an oil in which said compounds are dissolved unless the method of treating or stabilization forms therewith copper compounds less soluble than copper ethyl mercaptide. For example, after a cracked naphtha has been in contact with copper oxide, copper carbonate or coppervphosphate, sensitive tests show the presence of traces of copper remaining in the naphtha, whereas a It will be seen from the values listed in Table I that complete removal of copper from an oil may not be accomplished by contacting said oil with a reagent to form any of the copper salts listed. This fact is based on experimental data which proves that the deterioration of an 011 due to dissolved copper is not prevented unless the copper content of said oil is reduced to a value less than 0.1 p. p. m. as shown in Table H.

Turn It 4 on a! Color alter Appearance Hydrocarbon oil Dissolved copper 00 or 7 days aiter 30 days storage storage Pam per million West Texas cracked gasolin 10 +25 l0 Dark brown. Do. 1 +25 -l0 Do. Do. 0.1. +25 +12 -l6 color. Do Lem than 0.l..--.-. +25 +23 +21 color. Do. Zer +23 +23 +21 color.

portion of the'same naphtha. after prolonged contact with copper methyl mercaptide shows no evidence of dissolved copper compounds. Further, the small amounts of copper salts pres--- ent in a cracked gasoline which has been sweet- ,said oil in order to reduce the amount of dissolved copper to a value less than 0.1 p. p. m.

by converting the copper present in the oil into compounds with oil solubility less than the oilsoiubility of copper-ethyl mercaptide.

As examples of the practice oi' my invention, the following examples are described:

Example I A sample of cracked gasoline which had been sweetened by treatment with a solution containshaken until the oil was saturated with the copper compound and an excess remained. Portions of this gasoline were then treated with various reagents to form copper salts less soluble than copper ethyl mercaptide. Samples of each portion-oi gasoline stabilized with the various reagents were then stored'for comparison with a stored sample of the original gasoline and with the original gasoline saturated with copper ethyl mercaptide. The tabulation of results is ing cupric chloride was separated from the copper given below: reagent and divided into two parts. One part Tam III Color aiter Color alter No. Gasoline samples Copper an a w 1 am' so days storage storage 1 Caged gasoline, no additional treat- Negative; +24 2 +21 2 Cracked gasoline, saturated with-solid Positive, a iprox. +34 -1 oopper-ethyl-mercaptide. 0.1 P. P. 3 #2 sample, added 0. percent methyl Negative less than +24 +22 +21 mercgatan iollowed y water wash. 0.1 P. P. M. 4 #2 lam plus 2 percent sour vapor re Negative, less than +24 +21 +20 covery gasoline containing 0.01 percent 0.1 P. P. M. methyl mercsptan. 5 #2 sample, intimately contacted with Negative, less than +24 +21 +2 kaline aqueous solution oi dithimne. 0.1 P. P. M. 6 sample, can ted with ammoniacal Negative, less than +24 +22 +21 solution oi alpha-bensoinoxime. 0.1 P. P. M. 7 I2 sample, contacted with aqueous solu- Negative, less than +l +2! +21 tion oi thicnalidc. .1 P. P. M. 8 #2 sample, contactedwith aqueous solu- Negative, less than +24 2 tion oi iiJ-dibromohydroxyquinoline. 0.1 P. P. M.

9 sample, contacted with ammoniacal Negative, less than +24 +22 +2 solution oi diethyldithiocarbcnate. 0.1 P. P. M. 4

was stored without further treatment. To the other portion was added a solution of methyl mercaptan in sulfur-free hexane solution, the quantity added being suiilcient to cause the gasoline to have a methyl mercaptan content of 0.003 weight per cent. Alter the addition of the mercaptan, the gasoline was allowed to stand for two hours, after which it was washed with water and stored. The results of this stabilizing treat-' ment are shown below:

examples are illustrative of the manner in which deterioration is prevented in hydrocar- Ooloraiter Appearance Gasoline samples Copper test 253' 7 days aitswdays' storage storage Cracked gasolim,unstabiliaed. Positive greater +24 16 Darkbrown,

than 1 P. M. grainy. Cracked gasoline plus 0.003 percent methyl New" lea than +24 +23 color.

nrercaptan. 0.1 P. .M.

1 This gasoline was doctor sweet; no trabs oi mercaptanaiter two days.

Example II A sample of the same gasoline described Example I was similarly treated except that the stabilizing reaction was brought about by the addition to one portion 0! the gasoline of sufll-' cient sour vapor recovery gasoline to amount to 2 per cent by volume. This vapor recovery gasolinecontained approximately .01 weight per cent of methyl mercaptan. The results of this stabilization are illustrated'below; adding a small amount oi methyl mercaptan to m. W Orachad violins, copper awed. unatabilisei 2m greater +a -m Dark cameraman? ata:

This gasolincwasdoctor m. r

Example the said oil to form the less soluble copper methyl To a sample 0! doctor sweet cracked gasoline was added solid copper ethyl mercaptide and mercaptide, and removingthe copper -methyl mercaptide from the oil.

3. A process for treating hydrocarbon oil sweetened with copper reagents to prevent deterioration due to retained oil-soluble copper salts, which comprises contacting said oil with a sumcient quantity of a reagent comprising methyl mercaptan to reduce the concentration of the copper in the oil below that in a saturated solution or copper ethyl mercaptide.

4. A process for treating hydrocarbon oil sweetened with copper reagents to prevent deterioration due to retained oil-soluble copper salts, which comprises contacting said 011 with a sum- -cient quantity 01' a reagent comprising methylmercaptan to reduce the concentration of the copper in the oil below the critical value of 0.1 part per million.

WALTER A. SCHULZE. GRAHAM H. SHORT..

CERTIFICATE OF CORRECTION. Patent No. 2,222,122. November 19, 191m.

WALTER A. SCHULZE, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correctiori as follows: Page 1, $90 ond column, line 1+1, for "Cupper" read -Copper--; page 2, Table 1 1, in the column headed "Original Color'T, last line thereof, for +23" read +25; and that the said Letters Patent should be read with this oerrection therein that the same may conform to the record of the case in the Patent orriee.

Signed and sealed. this 21st day of January, A. D.-..l9hl.

Henry Van v Arsdale,

(Seal) Acting Commissioner of Patents. 

